The present invention relates to a power amplifier circuit and operation method thereof. More specifically, the present invention relates to a multi-frequency and multi-mode power amplifier circuit and operation method thereof.
As people are anxious for the transmission volume of wireless communication system, high level digital modulating method starts to be widely used. The congenital modulating nature of the digital modulation requires that the power amplifier has higher peak-to-average output power ratio. In the case of general system and environment, in most of the time the traditional power amplifier operates at an average output power region with low efficiency, and larger peak-to-average output power ratio means the power amplifier will face even lower operation efficiency. This means the power amplifier becomes an element of low operation efficiency as digital modulating method becomes high level.
Unfortunately, the high power consumption nature of power amplifier usually consumes ⅓-½ electricity of the entire communication equipment. Therefore for cell phones and the alike terminal equipments, low operation efficiency shortens standby and communication time. For base stations and the alike central office equipments, besides the increase on the electricity bill of telecommunication business owns, the costs spending on cooling and large power equipments increase as well. Therefore, keeping the power amplifier maintaining a certain high efficiency in all average-to-peak output power region has been a demand of new generation power amplifier.
Doherty power amplifier, which is one of the solutions for such demand, has been a hot research subject either in research papers or in patent field in recent years. Besides the congenital high efficiency, which is needed as described above, this amplifier has been proved by many research results on circuit linearization and minimization. Under the trend towards multi-frequency and multi-mode mobile communications, power amplifiers not only advance towards multi-frequency, and also needs to have adjustable average-to-peak output power point to meet the multi-mode operation needs. However, the Doherty amplifiers commonly available on the market mostly are of single-frequency and single-mode operation, the future of which is more and more facing challenge. Although a few patents, such as the United States Patent U.S. Pat. No. 6,137,355 provided single-frequency and dual-mode operation, the patent mentioned to adjust the effective size and operation class (for example, A, AB and B classes in transistor operation) of active element through bias, so that the power amplifier is switched between high linearity mode and high efficiency mode. However, there is no the feature of adjustable average-to-peak output power point because of no external circuits that Doherty power amplifier needed. Moreover, more groups of bias control circuits are required; and therefore the design complexity is increased and is only limited to single-frequency operation in frequency aspect.